It is known to provide composite plates in a laminate construction in which a core is provided with at least one layer and the latter can include a cover layer which is designed to impart a given esthetic nature to the plate and/or is intended for decorative purposes. Rounded edge beads along an edge of the plate are also required in certain applications, e.g. to limit the run-off of water over the edge and the cover layer can extend over the rounded bead.
The plates can be structural elements or decorative elements and can be utilized in building structures or in furniture, cabinetry or the like.
Customarily the core is composed of a low-cost material and itself can be a laminate, composite, e.g. consisting of chipboard or particle board, although other core materials such as natural wood or synthetic resins may also be used.
The outer surface of the core is provided with one or more layers by lamination, generally by gluing or other adhesive bonding to apply a decorative and/or protective layer in the form of a cover foil or sheet.
Composite plates with which the invention is concerned thus include decorative plates such as the high pressure laminates (HPL plates of German industrial standard DIN 16926). Decorative plates or boards from thermoplastic or thermosetting material can also be provided with protective coatings or layers which are glued to the core and which are water and heat resistant.
While the outer surface of the composite plate may be designed for a desired decorative effect and can be provided with a protective covering, the inner surface or the inwardly turned surfaces is generally provided with a synthetic resin foil allowing protection against moisture incursion and the effect of heating.
This foil also should be, therefore, water and heat resistant.
Naturally, in addition to or in place of this protective foil, the underside or inwardly turned surface of the composite plate or board can be provided with a decorative layer or plate, preferably a high pressure laminate plate or sheet.
The composite plates or boards described have been long known in the art and are increasingly finding interest when at least one edge of the board is rounded to form a bead.
Edge rounding and beading is ergonomically of interest and is of interest also for soft-line decor and for other esthetic reasons. Rounded edge beads are also valuable for window sills, roofing, decking and like purposes where, inter alia, a raised but rounded bead may serve to retard water run-off along an edge.
In the composite plate of U.S. Pat. No. 2,648,370 which is provided with an edge bead, the edge portion is a member separate from the core plate and which defines the edge bead and is glued to the core plate. The surfacing plate or foil, which is applied to the previously glued core plate is bent around the edge portion and glued thereto.
Fabrication is difficult for this composite plate and because the edge portion is a separate member, difficulties are often created by misalignment or the like during fabrication. Furthermore, it is difficult to provide the underside of the core plate and the edge portion with a protective foil.
The use of two separate parts for the core plate and the edge portion creates difficulties with respect to flush-fitting of the parts which may result in distortion of the decorative sheet and problems in the transition region between the parts. As a practical matter one is more often than not able to discern in the proper light a discontinuity in the surface.
Similar problems are encountered with the assembly described in U.S. Pat. No. 2,542,860 where a similar relationship prevails.
Another composite plate with an edge bead, as well as a method of making the composite plate, are described in German patent document--Open Application DE-OS No. 31 31 820. It is this earlier system which is the point from which the present invention proceeds.
In this system, the edge portion is formed entirely with the core plate and the shape of the edge portion is given to it by bending a part of the core plate so as to establish the edge bead. The edge and the remainder of the core plate at the outer surface are glued and the decorative sheet or laminate is applied and bent around the edge portion and glued to the latter while extending at the lower edge of the edge portion.
A groove is formed in the underside of the core plate directly adjacent the lower edge of the edge portion and inclines inwardly and upwardly at the upper surface. To avoid distortion of the decorative sheet, the depth of this groove is so dimensioned that a small amount of material of the core plate remains between the end of the groove and the decorative sheet at the upper surface of the core plate. Thereafter, the groove is widened at its mouth in a wedge shape, thereby bending the edge portion relative to the remainder of the core plate to form the edge bead. While the gluing of the decorative sheet at the core plate here poses no problems and no difficulties are encountered with respect to the flush connection between the core plate and the edge portion, because the edge portion is formed as part of the core plate, difficulties are nevertheless encountered both with respect to the mechanical results and the esthetic results. The filling of the groove is visible from the under or inner surface of the slab and from the side and the filling may provide a water droplet groove which is visible from the side. As a consequence, the optical characteristics of the plate, especially as seen from the side, are not generally satisfactory.
The very thin piece of core plate which remains and is bent during the bending of the edge bead upwardly, frequently is distorted and this distortion can be visible under some lighting conditions at the decorative sheet or through the latter.
Finally, mention may be made of the composite plates with rounded edges which are described in German Utility Model DE-GM No. 73 04 666, German Printed Application DE-AS No. 20 47 213 and German Open Application DE-OS No. 21 29 828 in which a groove is horizontally spaced from the edge of the core plate and is cut into the latter and is filled.
These composite plates, however, do not have upstanding rounded edge beads and are directed to attack on other problems and are concerned with significantly different systems from those which concern the present invention.